Embodiments disclosed herein relate generally to aircraft energy management systems including environmental control systems and more particularly to methods and apparatus for extracting fan discharge air to boost an aircraft environmental control system.
Turbine-powered aircraft conventionally incorporate environmental control systems (ECS) which control aircraft cabin temperature by the amount and temperature of a bleed air extracted from an engine. Historically, ECS have used engine bleed air that is extracted from a high pressure compressor (HPC) or is generated by means of a compressor that is driven by an auxiliary gas turbine (“APU”), throttled (pressure reduced), and cooled by a heat exchanger (“precooler”) using fan bleed air. Bleed air is also used to provide anti-icing to the aircraft, and must be at high temperature for this purpose—typically about 204° C. (400° F.).
Aircraft weight is a current concern in the current industry, with a decrease in aircraft weight resulting in an efficiency increase. In light of the concern, future aircraft will replace some or all of their metallic structures with composite materials to reduce weight and improve overall efficiency. These structures have limited temperature capability compared to metal alloys. For example, a typical carbon-fiber composite material may have a temperature limit substantially below 93° C. (200° F.). Conventional ECS interfaces, utilizing engine bleed air cannot meet this requirement without significantly increasing the size of an included precooler. Furthermore, composite aircraft will often use electrically powered anti-ice systems and therefore do not require high temperature bleed air.
One way ECS requirements have been met in composite aircraft, is by using electrically driven ECS to pressurize and condition ambient air. While effective to provide low-pressure, low-temperature bleed air, this requires a separate air inlet to efficiently entrain ambient fresh air, an additional air intake for cooling and considerable electrical power to drive the ECS compressors. The electrical power requirements can require an undesirable increase in the size of the engine mounted generators. In addition, the air intakes will produce drag on the aircraft, translating to an increase in fuel burn and therefore cost of operation. These weight and drag penalties of electrically driven ECS are also of concern in smaller aircraft.
Accordingly, there is a need for an improved environmental control system and method for extracting engine discharge air that will reduce aircraft weight and minimize drag air penalties.